The frequency of a value is the ratio of times (often given as a %) a value appears in the sample compared to the total number of values in the sample.
F(i) = N(i) / N (x 100 for result in %)
N(i) = # of values for rank i
N = total # of values
The frequencies are often presented with a bar graph.
Note: the sum of all frequencies MUST be 100%
F(i) = N(i) / N (x 100 for result in %)
N(i) = # of values for rank i
N = total # of values
The frequencies are often presented with a bar graph.
Note: the sum of all frequencies MUST be 100%
Example using the ages of a sample of men:
The ages of the men in the sample are: 18, 19, 23, 25, 30, 30, 35, 36, 39, 45, 54, 66, 66, 66, 74
The ages of the men in the sample are: 18, 19, 23, 25, 30, 30, 35, 36, 39, 45, 54, 66, 66, 66, 74
 The frequency of men aged 18 is 1 out of 15 men = 6.7% of sampled men are aged 18
 The frequency of men aged 30 is 2 out of 15 = 13.3% of sampled men are aged 30
 The frequency of men aged 66 is 3 out of 15 = 20% of sampled men are aged 66
 Etc…
 Ranking all values from lowest (left) to highest (right)
 Cumulated frequency of each value = frequency of this value + sum of all frequencies of values to the left
 Note: the cumulated frequency of the last value MUST be 100%
Age  18  19  23  25  30  35  36  39  45  54  66  74  Number of values = 15 

The frequencies and/or cumulated frequencies can be plotted on a bar graph:
The bar graph allows to easily see that:
To create a frequency table using Excel:
Note: click to learn how to activate the "Data Analysis Toolpack" in Excel 2007 or Excel 2010. This "addin" set of tools is not activated by default on Excel. Once you have activated the "Analysis Pack" addin, creating a frequency table and the corresponding histogram is ... very quick! Just check out the lefthand YouTube video below to learn how to do manipulate frequencies and histogram on Excel. Otherwise, follow the steps indicated below (and righthand video demo below).
 The mode is 66 (the value appears 3 times)
 The distribution of frequencies does NOT follow a bellcurve: it is NOT normally distributed
To create a frequency table using Excel:
Note: click to learn how to activate the "Data Analysis Toolpack" in Excel 2007 or Excel 2010. This "addin" set of tools is not activated by default on Excel. Once you have activated the "Analysis Pack" addin, creating a frequency table and the corresponding histogram is ... very quick! Just check out the lefthand YouTube video below to learn how to do manipulate frequencies and histogram on Excel. Otherwise, follow the steps indicated below (and righthand video demo below).
Creating a frequency table WITH the "Data Analysis Toolpack" on
Excel: 
Creating a frequency table WITHOUT the "Data Analysis Toolpack" on Excel:

If you have NOT installed the Analysis Toolpack on Excel, watch the demo video above or follow the steps below to create a frequency table:
 Label cell A1 "original entries". In this example, the cells A2 thru A20 contain your 19 entries
 Label
cell B1 "sorted entries" and copy your entries (for example from A2 to
A20) in a new column (for example B2 to B20): highlight the entries in
the new column and sort them from lowest to highest (use the "sort"
function)
 Intervals:
 If you do not need any interval and want to see the frequencies of all your entries (see the example used above with the ages of men), leave column C blank and go directly to step 3
 If you need intervals (for ex: % of values between 0 and $50, % between $50 and $100, etc), label cell C1 "interval limits" and enter the interval limits in the new column (for example from C2 thru C6 if you have 5 intervals limits) starting with the lowest one (do not enter the outer limits of the intervals such as 0 for ex). For example, in front of the cell labelled "$100", Excel will calculate the % of values between $50 and $100, etc
 Label cell D1 "frequencies". In cell D2, enter =FREQUENCY(array,bins). For "array", select the sorted entries A1 thru A20. For "bins":
 If you have NO intervals, select again all the sorted entries B2 thru B20. In that case your formula will be =FREQUENCY(B2:B20,B2:B20)
 If you have intervals, select the cells listing the interval categories (e.g.: C1 thru C5). The formula will be =FREQUENCY(B2:B20,C2:C6)
 Important: make sure you have written a comma between the "array" and the "bins"
 Click "enter". You should see the value "1" appear
 Highlight the cell you need frequencies for:
 If you have NO interval, select D2 thru D20 and go to step 6
 If you have intervals, select D2 thru D6 only and go to step 6
 Hit F2 and press CTRL+SHIFT+ENTER. The frequencies should appear in column D. If you have no intervals and some values appear several times in column B, you will see the frequency for each value only once, and the value "0" in front of the repeated values
 Label cell H1 "total number of values" and type =COUNTA(B2:B20)
 Label
E1 "% frequencies". In E2, type =E2/19 (or whichever value is in cell
H1) and type "enter". Select E2, click "copy". Highlight E3 thru E20 and
click "paste". Finally, select the options for the column D to make
sure the results appear as %
 Label cell F1 "cumulated frequencies". In F2, type =D2. In F3, type =F2+D3. Then, repeat the formula for all empty "F" cells in front a each "D" cell: select F3, click "copy", then highlight cells F4 thru F20 and click "paste"
 Label cell G1 "% cumul. frequencies". Apply the steps #78 to create the list of % cumulated frequencies
 Delete the repeat values in columns D thru G. then select the frequencies to create a bar graph